It's all about the release. Most times if I'm having a problem, I can trace it directly back to a bad release. Make sure you're not 'tweaking' the pouch.
Stay rock steady with your hold hand and pinch the ammo itself not the pouch in front of the ammo. Work on getting your draw and release exactly the same every shot.
Hope this helps.
The above is good advice. You shooting "gangster" or vertical? There are a ton of videos on you tube that can really help you get it all straight in your mind. After you get an idea of what you should be doing, work on the mechanics of doing it. Practice practice and then practice. But practice doing it right.
I know depending on what frame I use I have to keep a good eye on how straight the bands are. Most of the time I do OTT with gypsy tabs which allows the ammo to clear frame differently than not using tabs. Just make sure the line from your frame to pouch is a solid straight line.
Thanks guys, I had a good look at what I was doing, I changed my release grip from finger tip to thumb against first knuckle and found the bands were slightly twisted sometimes, amongst other things, including dropping the frame slightly (I shoot gangster with this frame). Release is much smoother now. I'll keep practising.
Something that helped me out in the beginning was a mirror. I set up and pulled the bands into position and turned to look in a mirror. My sling wasn't parallel to the target because my top fork tip (gangster hold) was pushed forward to the target. I'm consistent now with my position and I don't see fork hits.